sooty tailpipe (civic 88)

Hi group,

I have noticed that my tailpipe is sooty, and would like to hear your
input on possible causes. The Civic is an '88 (fuel injected) with 135k
miles, and runs well considering its age. I have a suspicion that the
mixture is too rich.

A few datapoints that might give additional hints:

- smog check (California) last year passed, but with less headroom than
earlier. Most values were in their usual very-low spots, except HC.

- gas mileage has dropped. I'm now at around 34/35 mpg (70% city/30
freeway), whereas I used to be closer to 40mpg, sometimes over.

- tailpipe is black; after a short trip, dark liquid drops from it.

- exhaust gas seems about normal. It's not white, it's not blue, it's
barely visible, it doesn't smell way out of the ordinary.

- no check engine light, ECU seems happy enough.

- it burns oil, a little bit. I get by without top-offs between oil
changes, though. Guess this is to be expected for mileage/age.

Any hints are appreciated. I'm probably going to take it to the mechanic
in a little while to get a 15k tuneup. Being able to give him hints
would be nice

Thanks!
TomB

 

Has your car ever had the purge kit update? This update kit includes new
injectors which solved a rich running problem on my '88 Civic.

Eric

 

Hello Eric,

Nope, it hasn't. Excuse my ignorance... what is a purge kit? I googled
around and all I could find was references to nitrous add-ons. I think
my little old faithful would disintegrate if you threw nitrous at it
It's stock, no mods of any kind (except a homebrew continous speed
electronic control for the vent blower, to replace a broken blower
resistor pack

 

The following is from a Tech2Tech TSB and describes the problem for 88-91
Civics with throttle body injection...

High CO and HC at Both Idle and 2500 RPM
SYMPTOM
The car is running at a high reading on both car-bon monoxide (CO) and
hydrocarbons (HC). The readings are high at low RPM and high RPM. The
readings may even be higher at high RPMs.

Typically all the other engine parameters are normal such as:
•Map Input Voltage .9-1.05 Volts
•Auxiliary Fuel Injector (below throttle plate injector) 2 ms
•Oxygen Sensor Voltage .8-.9 Volts
•Fuel Pressure 36-40 PSI
•Throttle Position Sensor Sweep .45 - 4.5 Volts

Under these conditions the car should not be running rich! The Manifold
Absolute Pressure (MAP) sensor voltage is nice and low. The injector pulse
width (PW) should not be delivering too much fuel at a PW of 2ms, yet too
much fuel is being delivered to the engine. If you disconnect the main
injector, located at the top of the throttle body, it will still run rich.

THE CAUSE
Apparently the injectors start leaking in the throttle body and let fuel
come in around the in-jector base o-rings. The key here is that the car is
getting way too much fuel, yet the PW is normal. When this happens the car
will run rich most all the time. The engine control module (ECM) tries to
maintain control by cutting the PW back, but it still runs way too rich.

THE FIX
The fix for this car is to replace the injectors. There is actually a
bulletin that covers this prob-lem, TSB 93-009. When you read the bulletin
you would think the only thing that the repair kit contains is a new purge
line; however, the kit also has both injectors in it for a reasonable price.
The repair kit is part number 04103-SH3-K30, and it includes both new
injectors.

 

Eric wrote:

|| The following is from a Tech2Tech TSB and describes the problem for
|| 88-91 Civics with throttle body injection...

Snipped a whole bunch of Good Stuff.

Thanks much, Eric! Really appreciated - this looks like it could be it.
TomB